Ecology

Populations Population The number of individuals of a species in a specific habitat

Characteristics of Populations Three important characteristics of a population are its geographic distribution, describes the area inhabited density, and number of individuals per unit area growth rate.

Factors that change population size Birth: leads to an increase Death: leads to a decrease Needs to be balanced for population size to remain constant Immigration: leads to an increase Coming into a habitat Emigration: leads to a decrease Leaving a habitat

Exponential Growth individuals in a population reproduce at a constant rate Under ideal conditions with unlimited resources, a population will grow exponentially

Logistic Growth a population's growth slows or stops following a period of exponential growth resources become less available Population growth may slow down when the birthrate decreases, when the death rate increases, or when both events occur at the same rate population growth may slow down when the rate of immigration decreases, the rate of emigration increases, or both

Carrying Capacity size of the population when the average growth rate reaches zero That number, in turn, represents the largest number of individuals that a given environment can support

Quick Assessment Prompts: Answer the following using complete sentences: What factors can change a population size? What is the difference between exponential growth and logistic growth? Define Carrying Capacity.

Limits to Growth Limiting Factors factor that causes population growth to decrease

Density-Dependent Factors limiting factor that depends on population size Density-dependent limiting factors include competition, predation, parasitism, and disease.

Density-Independent Factors Unusual weather, natural disasters, seasonal cycles, and certain human activities are all examples of density-independent limiting factors Many species show a characteristic crash in population size

Quick Assessment Prompts: Answer the following using complete sentences: If an entire lynx population disappears, what is likely to happen to the hare population on which it preys? How does a limited resource affect the size of a population?

Changes in Pop. Size and Biodiversity Speciation and Extinction are influenced by: Natural causes (mutations, evolution) Changes in climate (adaptations needed) Human activity (deforestation, pollution) Introduction of invasive species Non-native species that move into a habitat and has devastating effects https://www.invasivespeciesinfo.gov/index.shtml

Example of Invasive Species Kudza Vine Introduced from Japan for erosion control (1876) and has been growing uncontrollably ever since Has no competitors for resources or predators Grows (in summer) almost a foot a day

Australia and Its Rabbits Rabbits were brought to Australia in for hunting and food ~ 1880s No natural predators Plenty of resources Within 6 years, there hundreds of thousands There are now about 300 million Destroying habitats Digs up root systems Developing deserts

Rabbit Solutions Hunting Rewards Fumigation (spraying poisons) Dynamite Plowed 2000 mile fence All Failed

Rabbit Solutions Introduced virus in 1951 (2nd invasive species) Killed millions But some were naturally resistant They survived and reproduced Bunnies are also resistant to virus (genetics) 1991, 1996: Introduced new viruses and killed many but same as above Decision to release a new virus every two years to lessen the population (or at least keep it in check)

Australian Rabbits Besides acting as an invasive species, the rabbits serve to demonstrate a second point: Co-evolution Two species that evolve in response to each other Rabbits obtain immunity to virus (through genetics) Virus evolves and begins killing again Rabbits again obtain immunity to virus (through genetics) This continues…